Contact Form 7 error sending message

Hi, I’m getting this standard message “There was an error trying to send your message. Please try again later.” when I press ‘Send’ on my form. The message has a red outline, which can according to the FAQS mean that the form “tried to send mail with wp_mail(), but it failed”. It advises to contact the hosters, which I’ve done, and they’ve sent this – I’ve no idea what it means and what to do about it and am hoping that someone here may be able to help:
“Can you change your code to send email to “localmail.4demail.com” using port “25” and authenticate using the login credentials for your email account (i.e. [email protected] and “password”)
and see if works?”
I’ve used this plugin repeatedly with other hosters with no issues so suspect that it is a problem withe mail servers, but am out of my depth!
Thanks, Helen